1. Field of the Invention
This invention pertains to an improved railroad signal system having standard red, yellow, and green lights as well as a white numbered aspect light, the numbered light indicating when a red light will change to yellow when approached at an allowable speed.
For a better understanding of the invention, a typical prior art signalling circuit is first described. It should be understood that in the following discussion only the elements directly associated with the invention are mentioned. The signalling system has various other components which have been omitted for the sake of clarity.
2. Description of the Prior Art
Railroad signal systems with red, yellow and green lights have been used extensively for a long time. In such systems usually a train could not pass a red light. The red light was indicative of a train in the adjacent blocks ahead. However, while this type of system was very safe, in congested areas it was impractical because it caused consecutive trains to be too far apart thereby increasing the minimum headway. This disadvantage was especially acute in railroads used for urban or suburban mass transportation such as subways. Therefore a modified system has been introduced in which at least one of the signal light housings included a white numbered light in addition to the standard red, yellow and green lights. The white numbered light also had a preselected speed associated therewith. This white numbered light indicates to the train operator that the signal would change from red to yellow and the light could then be passed at the preselected speed displayed by the white numbered light without the train being tripped. This type of modified system has been in use by the New York City Transit Authority. However, as shall be described more fully below, the system presently in use has a number of disadvantages. First, it requires an extra wire loop between signal housings. This loop increases the possibility of shorts in the wire especially since the wire has to pass frequently from one crowded terminal box to another, where it could be pinched easily. Thus, wire looping reduces the integrity and safety of the signal system. It is design policy to eliminate wire looping circuits where feasible. Also, the additional wire increases the cost of installation, maintaining and trouble shooting the system.